1. Field of the Invention
The present invention relates to a page description data processing apparatus, a page description data processing method, and a recording medium for performing a particular processing sequence on page description data having a certain attribute, from among page description data described by a page description language (PDL), for thereby converting the page description data into more robust page description data (hereinafter referred to as “fortified page description data”).
2. Description of the Related Art
In recent years, DTP processes for setting characters and images generated by a user via a computer into one or more electronic pages using DTP (Desktop Publishing) application software installed on the computer have been widely used in printing and platemaking fields.
Such DTP application software generates page description data, which express images of respective pages based on elements such as characters and images that are edited by the user.
Page description data are defined by vector data independent of the resolution of an output machine such as a printer, a platesetter, or the like, and such data cannot be output per se from the output machine. Therefore, the page description data are rasterized by a RIP (Raster Image Processor) into raster image data comprising a cluster of dots representative of elements such as characters and images in the pages.
When raster image data are supplied to the output machine such as a printer, a platesetter, or the like, the output machine outputs a hard copy or a printing plate, which carries an image based on the raster image data (see Japanese Laid-Open Patent Publication No. 2005-070957).
PDF (Portable Document File) version 1.3, which forms one type of page description data, incorporates therein a “dotted line pattern” operator for controlling a pattern of line elements and gaps, which are utilized in stroking a linear path. The term “path” refers to a path having no intrinsic line width, and which interconnects a start point and an end point. The term “stroke” refers to a process of applying a certain line width to a path.
Variables which can be set by the “dotted line pattern” operator include a “dotted line array” for designating a length for line elements and gaps that appear alternately, and a “dotted line phase” for designating a plotted state at the start point of a periodic dotted line. For details, reference should be made to PDF Reference, second edition, Adobe Portable Document Format Version 1.3, initial edition, 1st printing, published July, 2000, Author: Adobe Systems, Publisher: Pearson Education, ISBN 0-201-61588-6, pages 136 and 141-143. The terms “dotted line array” and “dotted line phase” may hereinafter be referred to collectively as “dotted line configuration parameters.”
The relationship between dotted line configuration parameters and a dotted line pattern that actually is plotted will be described in detail below with reference to FIG. 10A of the accompanying drawings, based on an example in which a linear path is stroked with 11 unit lengths from a start point to an end point thereof.
For example, in FIG. 10A, [4 2] {0} implies a coupling of parameters as a dotted line array [4 2] and a dotted line phase {0}. The dotted line array [4 2] represents turning-on of 4 successive unit lengths, followed by turning-off of 2 successive unit lengths. In other words, the dotted line pattern has a periodicity unit represented by 6 unit lengths. Stated otherwise, the dotted line pattern comprises a repetition of line elements, each of which are 4 unit lengths long, and gaps, each of which are 2 unit lengths long.
The dotted line phase {0} indicates that the above periodic dotted line pattern includes a phase shift of 0. The periodic dotted line pattern having such a dotted line phase {0} is illustrated in the upper section of FIG. 10A, whereas a periodic dotted line pattern having a dotted line phase {1} is illustrated in a middle section of FIG. 10A. The periodic dotted line pattern having the dotted line phase {1} is equivalent to the periodic dotted line pattern having the dotted line phase {0} if shifted one unit length to the left (toward the start point of the path). Similarly, a periodic dotted line pattern having a dotted line phase {2} is illustrated in a lower section of FIG. 10A, which is equivalent to the periodic dotted line pattern having the dotted line phase {0} if shifted two unit lengths to the left (toward the start point of the path).
According to PDF specifications, as illustrated above, the plotted configuration of a dotted line is determined sequentially based on a prescribed periodic repetition from the start point to the end point of the dotted line.
However, PDF specifications are susceptible to unexpected problems when a dotted line pattern generated along a linear path is rasterized.
For example, when the start point and the end point of each line element, i.e., the end point and the start point of each gap, are determined, the points may suffer a positional shift error, because the position of the start point or the end point differs from RIP to RIP. The positional shift error refers to a so-called processing error caused by different RIP processing algorithms or software versions. Accordingly, as shown in FIGS. 10B and 10C of the accompanying drawings, the number of generated line elements of one path may be different from the number of generated line elements of another path, even if the paths are of the same length.
In FIG. 10B, if an end point 202a of a line element 200a and an end point 202b of a line element 200b are different from each other due to processing errors, then a start point 206a of a line element 204a, which is adjacent to the line element 200a, exists at a position that lies beyond an end position 208 of the path, i.e., to the right side of the end position 208. Additionally, a start point 206b of a line element 204b, which is adjacent to the line element 200b, exists at a position that is not beyond the end position 208 of the path, i.e., to the left side of the end position 208.
FIG. 10C shows an upper dotted line, which is made up of the line element 200a and the next line element 204a, and a lower dotted line, which is made up of the line element 200b and the next line element 204b. The dotted lines are imparted with a certain line width by means of a stroking process.
As shown in FIG. 10C, a filled area 210a is formed around the line element 200a, and a filled area 210b also is formed around the line element 200b, according to a line width and a capping format (end processing format), which are preset in the stroking process.
However, a filled area is not formed around the next line element 204a following the start point 206a (the upper dotted line) because the start point 206a is positioned outside of the path. On the other hand, a filled area 212 having an oblong shape is formed around a portion of the next line element 204b following the start point 206b (the lower dotted line) because the start point 206b is positioned within the path.
As described above, when a dotted line pattern is formed along a linear path, a line element may be generated indeterminately in the vicinity of the end point of the linear path, depending on a combination of processing errors caused by the RIP processing algorithm, the software version, and dotted line configuration parameters. Consequently, the dotted line pattern may be converted unintentionally into a dotted line configuration. When the image data including the dotted line is rasterized, such an unintended dotted line configuration possibly may result in unexpected printing difficulties, the cause of which is difficult to analyze. Such a problem manifests itself in particular when the line width is large.